One challenging goal of biochemical microfluidics is the ability to build small, often thumbnail-sized chips capable of automatically performing assays that would otherwise require laboratory equipment, technicians, and hours of processing time. This requires shrinking the dimensions of samples and processing devices (e.g., ovens, mixtures, etc.) several orders of magnitude. Micro-electro-mechanical systems (MEMS) manufacturing techniques enable fabrication of a vast array of small, miniaturized features to be created on the chip. In this regard, MEMS offers the ability to create true laboratory-on-chip miniaturized devices. To realize their full potential, however, the device should not only control the location and composition of sub-microliter samples, but also the conditions such as temperature, pressure, and electrical signals in and around working fluids.
Certain biochemical assays and processes require particular thermal management requirements. For example, microfluidic devices have been used successfully for miniaturizing biochemical assay protocols that require thermal cycling such as polymerase chain reaction (PCR). Oft-cited advantages of using microscale fluid volumes include lower waste and reagent usage, faster processing time (e.g., rapid heating and cooling, shorter diffusion length), potentially higher throughput, efficiency, and levels of automation. For example, resistive heating and temperature-sensing elements can be integrated into microfluidic chips, often as thin-film platinum wires. While many reported lab-on-a-chip systems use integrated heating elements and temperature sensors to eliminating the need for macroscale thermal components (which add bulk and thermal crosstalk), they commonly require external pumps and valves for pressure-driven fluid handling. Interfacing macroscale tubes with microfluidic chips in inhibits scalability and parallelization.
Driving mechanisms such as externally applied pressure and electroosmosis can provide excellent control of flow rates in continuous flow microfluidic channels, but problems can arise due to excessive power consumption, analyte dispersion, and, for electrokinetic mechanisms, electrolysis and Joule heating in the working fluid.